In U.S. Pat. No. 6,220,611, granted Apr. 24, 2001, the applicant disclosed unique methods relating to pivoting and stowable wheel axle assemblies for wagons and carts, and related innovations. Improvements were further disclosed in the continuation-in-part U.S. patent application Ser. No. 09/604,769 (carrier and stroller devices) and other applications referenced above. This application provides further refinements and enhancements to foldable child and cargo carrier trailer and stroller devices with tow bars which include pivoting wheel axles. Many of the enhancements here relate to partly or fully covered enclosed child carrier devices, as well as folding, removable wall cargo carrier devices which may be trailed with a tow bar behind a separate device, or alternatively may be pushed or pulled.